At least 83 people were killed and more than 180 wounded in several blasts in Sayeda Zeinab, a largely Shi'ite southern suburb of Damascus, according to state news agency SANA.
The Syrian Observatory for Human Rights, a pro-opposition monitoring group, said two near-simultaneous attacks with explosive-rigged cars killed 59 people in the central city of Homs on Sunday.
Statements in the name of Islamic State, posted on social media, claimed responsibility for both attacks.
Footage from pro-Damascus television channels showed charred corpses buried by rubble, damage to shop fronts and debris littering a wide area. Plumes of smoke rose from burning cars and wounded people walked around dazed.
DPA was not able to authenticate the claims but they were consistent with previous statements by the group, including claims of responsibility for three other deadly attacks in the same areas since December.
People gather in the aftermath of a multiple explosive attack in the Sayyida Zeinab area, 10 km south of Damascus, Syria, Sunday, Feb. 21, 2016. Source: AAP
The explosions in Homs hit the city's al-Zahraa district, most of whose residents belong to President Bashar al-Assad's Alawite sect.
At least 39 of the dead were civilians, the Observatory said, with the identity of the others unclear.
Footage from SANA showed burned-out vehicles and damaged buildings around a crater in the street where one of the blasts took place.
SANA put the toll at 39.
The Observatory said that at least one car bomb and two suicide attackers wearing explosive belts were involved in the Sayeda Zeinab attacks.
The area, a government stronghold, is home to an important Shi'ite shrine. Pro-Iranian militias who have come to the aid of al-Assad's overstretched forces have boasted that they are defending the shrine.
The bombings come exactly a month after previous attacks that killed 71 people in Sayeda Zeinab, including 29 civilians and 42 pro-regime militiamen, according to figures published by the Observatory at the time.
Violence rages on unabated across the country as world powers and the United Nations push to end the five-year-old conflict, meeting in Geneva to try to broker a ceasefire.
A handout picture made available by the Syrian Arab News Agency (SANA) shows a wounded Syrian child at a hospital in Damascus, Syria, 21 February 2016. Source: AAP
Peace talks were suspended almost immediately earlier this month as Syrian government forces and their allies, backed by Russian air strikes, intensified assaults against insurgents in Aleppo province.
The latest fighting in the north of the country has displaced tens of thousands of people, many of whom headed for the Turkish border. The exodus added to more than 11 million already displaced by the conflict, which has claimed 250,000 lives.
